Versatile light‐responsive organogels: Evaluation of their dye releasing and photoinitiation behaviors

Light‐responsive crosslinked structures were prepared by a straightforward quaternization strategy using chloride functional polystyrene copolymers and commercially available Michler's ketone with varying feed ratios. Resulting organogels demonstrated excellent solvent absorption and their swelling characteristics were altered by UV‐light irradiation. According to scanning electron microscope images, UV‐illuminated samples showed an obvious photodecomposition, which enhanced their solvent uptake capacity with increase of UV exposure. Additionally, release behavior of eosin Y as a model compound was determined by UV–vis and fluorescence spectrometers. Achieved photoactive gels were also employed as the reusable heterogeneous initiators for photoinduced free‐radical polymerization of methyl methacrylate. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1275–1282     

An inverse coefficient problem for a quasilinear parabolic equation with periodic boundary and integral overdetermination condition

In this paper, the inverse problem of finding the time‐dependent coefficient of heat capacity together with the solution periodic boundary and integral overdetermination conditions is considered. Under some natural regularity and consistency conditions on the input data, the existence, uniqueness, and continuous dependence upon the data of the solution are shown. Some considerations on the numerical solution for this inverse problem are presented with an example. Copyright © 2014 John Wiley & Sons, Ltd.     

Backtracking and exchange of information: Methods to enhance a beam search algorithm for assembly line scheduling

Beam search (BS) is used as a heuristic to solve various combinatorial optimization problems, ranging from scheduling to assembly line balancing. In this paper, we develop a backtracking and an exchange-of-information (EOI) procedure to enhance the traditional beam search method. The backtracking enables us to return to previous solution states in the search process with the expectation of obtaining better solutions. The EOI is used to transfer information accumulated in a beam to other beams to yield improved solutions.     

Minimizing weighted mean absolute deviation of job completion times from their weighted mean

We address a single-machine scheduling problem where the objective is to minimize the weighted mean absolute deviation of job completion times from their weighted mean. This problem and its precursors aim to achieve the maximum admissible level of service equity. It has been shown earlier that the unweighted version of this problem is NP-hard in the ordinary sense. For that version, a pseudo-polynomial time dynamic program and a 2-approximate algorithm are available. However, not much (except for an important solution property) exists for the weighted version. In this paper, we establish the relationship between the optimal solution to the weighted problem and a related one in which the deviations are measured from the weighted median (rather than the mean) of the job completion times; this generalizes the 2-approximation result mentioned above. We proceed to give a pseudo-polynomial time dynamic program, establishing the ordinary NP-hardness of the problem in general. We then present a fully-polynomial time approximation scheme as well. Finally, we report the findings from a limited computational study on the heuristic solution of the general problem. Our results specialize easily to the unweighted case; they also lead to an approximation of the set of schedules that are efficient with respect to both the weighted mean absolute deviation and the weighted mean completion time.     

Hydrogen-bonded layer-by-layer films of block copolymer micelles with pH-responsive cores

The structure of grafted adsorbing polymers on surfaces is described as a statistical ensemble of loops generated by an one-dimensional random walk perpendicular to the surface. The configuration of each chain is considered as a succession of closed loops ended by an open loop (a tail). The probability of formation of each individual loop is the product between the probability of first return to the surface and a Boltzmann factor containing the free energy of the Flory-Huggins kind, which is approximated by the minimum free energy of all possible configurations of that loop. At high grafting densities, the attractive interactions between monomers and surface control the fraction of polymer belonging to either closed loops or tails, hence the formation of a stretched grafted brush. At low grafting densities, the increase of that interaction above a critical value generates an abrupt collapse of the brush on the surface. Whereas for long polymers (with more than about 100 Kuhn segments), the structure of the brush can be determined, in general, only via Monte-Carlo sampling, it is argued that the two structural transitions indicated above can be well predicted by simple approximations.     

Effect of structural isomerism and polymer end group on the pH-stability of hydrogen-bonded multilayers

Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9-12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.     

In vitro antiprotozoal activity of extracts of five Turkish Lamiaceae species

The in vitro antiprotozoal activities of crude methanolic extracts from the aerial parts of five Lamiaceae plants (Salvia tomentosa, S. sclarea, S. dichroantha, Nepeta nuda subsp. nuda and Marrubium astracanicum subsp. macrodon) were evaluated against four parasitic protozoa, i.e. Trypanosoma brucei rhodesiense, T. cruzi, Leishmania donovani and Plasmodium falciparum. The cytotoxic potentials of the extracts on L6 cells were also evaluated. Melarsoprol, benznidazole, miltefosine, chloroquine and podophyllotoxin were used as reference drugs. All crude MeOH extracts showed antiprotozoal potential against at least three parasites, so they were dispersed in water and partitioned against n-hexane and chloroform to yield three subextracts that were screened in the same test systems. The n-hexane extract of N. nuda was the most active against T. brucei rhodesiense while the CHCl3 extracts of S. tomentosa and S. dichroantha showed significant activity against L. donovani. All organic extracts displayed in vitro antimalarial and moderate trypanocidal activities against T. cruzi with the n-hexane extract of S. sclarea being the most active against the latter. The extracts displayed low or no cytotoxicity towards mammalian L6 cells.     

A Class of 3-dimensional Contact Metric Manifolds

We classify the contact metric 3-manifolds such that ${||{\rm grad}{\lambda}|| = 1 \, {\rm and} \, \nabla{\xi}{\tau} = 2a{\tau}{\phi}}$ .